!!URGENT!! master cylinder issues....

Post by **callyspoy** » Wed Apr 23, 2008 11:36 pm

hi folks, im off to santa pod with my friends on friday(its a vdub thang...i know...) but, as much as everything is working fine, the master cylinder is leaking something chronic, and has done since i changed all the brakes etc.
problem lies here...
i fitted a remote reservoir, disc brakes, and new seals in the master cylinder(the correct ones!) and removed the little rubber from the master cylinder because of the discs.
it seems to be leaking from the front of the master, where the push rod is etc, and i am massively baffled.

my thoughts were...
will removing the little rubber have any negative effect on sealing?
could the remote reservoir be having any negative effect(clutching at straws a little with that one!!)

i need it fixed tomorrow really, and i truly cant see what could be wrong. the cap is sealed also! it IS coming from the front, could i just have got a bad set of rubber seals? or are there other bits that can wear out in the master?
speedy responses will be greatly appreciated, although i won't be on until 4ish tomorrow(thursday), the reason for this is i can order some bits if necessary!
cheers folks
*Callum*

Post by **bigginger** » Wed Apr 23, 2008 11:42 pm

The bore of the cylinder can wear, meaning that it doesn't seal correctly, new rubbers or not. That's anecdotal, btw - not been there myself.

Post by **Packedup** » Wed Apr 23, 2008 11:44 pm

It could be bad seals - Which could in turn be because of a worn master. If after doing the various jobs you bled the brakes by pumping the pedal, there's a chance the seals had to pass over a ridge caused by wear over the years. The piston normally travels over quite a short distance, not the whole length of the bore. So eventually the cylinder wears at one end, whilst remaining the original bore further down. When the rubber seals travel over this ridge they can get damaged, leading to leaks and general not good brake issues.

You could try a new set of seals and an alternate method of bleeding (eg Ezibleed), but it might be better and less time consuming in the long run (not to mention possibly safer) to get a new master.

Post by **callyspoy** » Wed Apr 23, 2008 11:52 pm

i see...well i do have a different master cylinder that i can try, not new, but it may not have the same problem. the thing was though, it was needing topping up every week, now its more like every day! it just seems odd...so i took it apart earlier today, and it is still very bad. so we think try the different master?

Post by **bmcecosse** » Thu Apr 24, 2008 12:18 am

Are you sure you removed the correct seal when you modified it for the disc braking ? Also there are two bore sizes for master cyls - did you get the correct seals for whatever bore you have ? But likely as others have said the bore is worn or rusted and has damaged the seals. Sorry to say another master will probably be needed.

Post by **callyspoy** » Thu Apr 24, 2008 12:20 am

hi bmc, yes they are the correct size. and the rubber is the little one that sits inside the "cup" yes?

Post by **bmcecosse** » Thu Apr 24, 2008 12:26 am

I really don't know - the 'top hat' seal they say. It's a job I have never done - not using disc brakes you see!!

Post by **callyspoy** » Thu Apr 24, 2008 12:43 am

aaah i see, certainly has got a hat look about it, so i'm assuming its the right one!

Post by **Packedup** » Thu Apr 24, 2008 12:47 am

If you can get your hands on one, you might want to try a cylinder hone on it. Provided you don't have to buy one, it's a free way of seeing if the master is recoverable

I saw a diagram somewhere of master cylinder seals - The top hat one that needs removing looks very much like a top hat - None of the other seals do! It's the one near the back of the cylinder, the idea being it holds a residual pressure in the system. With drums that's a good thing, but with discs it's bad as it keeps the pads dragging on the discs all the time.

Post by **Stig** » Thu Apr 24, 2008 8:07 am

callyspoy wrote:hi bmc, yes they are the correct size. and the rubber is the little one that sits inside the "cup" yes?

That's the one, I vaguely remember it being a bit smaller than the others too.

Post by **callyspoy** » Thu Apr 24, 2008 5:02 pm

thanks guys. ive ordered some new seals today, should *fingers crossed* get them tomorrow, will then fit the other master and hope for the best, genuinely cant be worse than i have at the moment!

Post by **IslipMinor** » Fri Apr 25, 2008 2:06 pm

Callum,

The valve that needs removing for discs is on the end of the spring inside the master cylinder, the opposite end to the seals. It's about 10/12mm in diameter.

Post by **Kevin** » Fri Apr 25, 2008 3:31 pm

the master cylinder is leaking something chronic, and has done since i changed all the brakes etc.

Well that should have given a clue that something was not right.

ive ordered some new seals today, should *fingers crossed* get them tomorrow, will then fit the other master and hope for the best, genuinely cant be worse than i have at the moment!

But you haven't said whether you have actually checked the bores to make sure everything is in excellent order, sorry to say it but just fitting new seals with fingers crossed is asking for trouble and I would think a new master cylinder is on the cards, sorry if I sound rather negative but the 2 most important things to me are steering and stopping.

Post by **rayofleamington** » Sat Apr 26, 2008 8:08 pm

99% of m/c failures seem to be when the m/c is corroded. The corrosion happens quickest where the bore is open to the elements (via the boot).
If the m/c bore is corroded here, the secondary seal will leak and fluid leaks out to the m/c. The leaked fluid is often replaced by air and can usually be seen by an air bubble rising into the reservoir when pressing the pedal. Don't press too aggressively when looking as there will be a small brake fluid fountain at the start of the stroke!

The worst thing I vere did was fit new seals to a good m/c. The seal kit was not fit for purpose and in the process of many many trial fits I sctratched the m/c bore. I thought all was well until reaching Spain (on the way to Gambia) where the scratch had damaged the seal and had totla brake failure. I had to order a replacement new cylinder with expensive next day European delivery (more expensive than the parts), and continued to curse myself for doing the seal kit job anyway and also for not having the time to reprimand the supplier that gave me the parts which nearly caused a severe accident.

My tendency would be to never do a replacment m/c seal kit as the price of replacing the whole thing is worth peace of mind.
Having said that I've done approx 10 m/c replacements and one of the new m/c's was faulty too (never gave a good pedal and had to be replaced 2 years later).

Post by **callyspoy** » Sun Apr 27, 2008 7:57 pm

well...i did the swap, got to northampton and back with no fluid loss, brakes are tight, im a happy bunny! had my points not opening though, that wasnt funny! but all in all, a successful first 'long' voyage in impy, which is nice!

Post by **bmcecosse** » Sun Apr 27, 2008 10:33 pm

Well done.